1. Field of the Invention
The present invention relates to a braking control device for adjusting a fluid pressure according to the degree of opening of a proportional electromagnetic valve driven at a set drive frequency, and controlling a braking force on the basis of the adjusted fluid pressure.
2. Description of the Related Art
Conventional control devices are known in which an excitation current is applied to a linear solenoid to control the driving of a proportional electromagnetic valve, and the object being controlled is controlled by the proportional electromagnetic valve. In one application of this technique, a proportional electromagnetic valve is provided in a braking control device of a vehicle. In such a braking control device, a predetermined current as a control signal is fed from a control device to the linear solenoid of the proportional electromagnetic valve, whereby the proportional electromagnetic valve actuates and opens and closes an oil channel, and the flow rate or hydraulic pressure of the oil is adjusted. In this type of braking control device, noise is sometimes generated by wide fluctuations in hydraulic pressure between the upstream side (master cylinder side) and downstream side (wheel cylinder side) of the proportional electromagnetic valve. Vehicle braking force maintaining devices (hereinafter referred to as braking force maintaining devices) have therefore been developed that are capable of suppressing the occurrence of such noise (Patent Document 1, for example).
In the braking force maintaining device described in Patent Document 1, the control frequency of duty control for controlling the opening and closing of the electromagnetic valve is set to a low value (20 Hz) when the brake fluid pressure of the channel downstream from the electromagnetic valve is higher than a predetermined pressure (3 MPa), i.e., when the braking force that had been maintained in order to prevent movement of the vehicle is still large. When the brake fluid pressure of the channel downstream from the electromagnetic valve is at or below the predetermined pressure (3 MPa), i.e., when a certain amount of braking force remains, the control frequency of duty control for controlling the opening and closing of the electromagnetic valve is set somewhat high (60 Hz). When the brake fluid pressure of the channel downstream from the electromagnetic valve has been adequately reduced (to 0.3 MPa or lower), the control frequency of duty control for controlling the opening and closing of the electromagnetic valve is set to an extremely high value (1 kHz).